With the recent spread of digital video cameras and digital cameras, the demand for color printers for printing color images obtained by these cameras is increasing. Although various systems are known as printing systems of such printers, an inkjet system is particularly attracting attention recently because, e.g., non-contact printing can be performed for a printing medium such as a paper sheet, color images are readily obtainable, and the noise is low. As the construction of this inkjet printer, a serial printing apparatus is generally widely used because the apparatus is inexpensive and can be made compact. This serial printing apparatus includes a printhead which discharges ink in accordance with desired printing information, and prints an image while scanning back and forth in a direction perpendicular to the feeding direction of a printing medium such as a paper sheet.
One color printer printing method is a method by which an ink sheet coated with heat-sublimating or hot-melt ink is selectively heated by a thermal head to transfer the ink image onto a printing sheet. In particular, a sublimation type heat transfer printing apparatus is expected as a color printer for a digital camera, since high-quality, full-color images can be obtained.
Generally, a heat transfer printing apparatus prints an image of a plurality of colors by moving a printing sheet back and forth. Therefore, it is necessary to held printing sheets during printing. Since this forms partial blank portions in which no images can be printed, an image cannot be printed on the entire surface of a printing sheet, unlike silver halide photographs. Some large-sized apparatuses for business use realize full-surface printing on an output printing sheet by using rolled printing paper and a built-in cutter.
Unfortunately, these apparatuses using rolled paper and having a built-in cutter are large and expensive. Therefore, the following method is known as a method by which a printed product having an image printed on the entire surface of a printing sheet is easily obtained by the use of a small-sized, inexpensive apparatus. This method uses printing paper having perforations for allowing easy cutting formed on the two sides in the conveyance direction of the sheet. Also, an image which is a size lager than a final printing sheet size cut from the perforations is printed. After the image is printed, the printing sheet is cut from the perforations to obtain a printed product (with no blanks) having an image printed on the entire surface of the printing sheet like a silver halide photograph. FIG. 2 shows an example of a printing sheet used in this method.
This printing sheet has a predetermined size. In addition, heat transfer printing generally prints a full-color image by printing images of a plurality colors by moving a printing sheet back and forth. So, an ink sheet for use in printing also has a predetermined size corresponding to the size of the sheet and is coated with inks of different colors for each predetermined width. FIG. 13 shows an example of an ink sheet. Referring to FIG. 13, on a band-like base 130, yellow ink layers Y, magenta ink layers M, and cyan ink layers C are repetitively arranged in repetitive units U in the longitudinal direction of the base 130. These inks layers of three colors can be arranged in an arbitrary order. Also, these color ink layers can be formed close to each other or with appropriate intervals between them. Alternatively, the ink layers can slightly overlap each other as long as no practical problem arises. Furthermore, black ink layers can be added to the repetitive units U.
As described above, the size of an ink sheet is determined in accordance with the size of a printing sheet. To obtain a printed product of a different size, therefore, it is necessary to prepare a printing sheet and ink sheet corresponding to that size. Accordingly, to obtain printed products of a plurality of different sizes, it is necessary to prepare printing sheets and ink sheets corresponding to these sizes.
Also, the above-mentioned apparatus for business use which has rolled printing paper and a built-in cutter can cut the printing sheet in a given length in the paper feeding direction. Hence, printed products of different sizes having almost arbitrary lengths in the paper feeding direction can be obtained.
As shown in FIG. 13 described above, however, an ink sheet is generally formed by repetitively arranging color ink layers in repetitive units U on a sheet having a predetermined size. If printing sizes are different, therefore, it is necessary to prepare ink sheets coated with color ink layers in accordance with these printing sizes. On the other hand, printed products differing in size can be obtained by the same ink sheet in some cases. In these cases, the size of a printed product is always equal to or smaller than the ink sheet size, so unused ink is wasted. For example, when a printed product having a size half that of an ink sheet is formed, the half of ink is wasted. When a printed product having a size ¾ the size of an ink sheet is formed, the ¼ of ink is wasted.
As described above, when printed products differing in size are formed using ink sheets of the same size without using ink sheets of different sizes, ink not used in printing is wasted.